As a conventional image forming device that employs an electrophotographic system, there is known a printer provided with a photosensitive member, and a developer cartridge that supplies toner to the photosensitive member.
This type of printer is also provided with sensing means for detecting information on the mounted developing cartridge (whether the developing cartridge is a new product, for example).
According to one method that has been proposed for determining information about a developing cartridge, a rotary body is rotatably provided in the developing cartridge and has a contact protrusion that contacts a sensing arm in a main casing of an image forming device. When the developing cartridge is mounted in the main casing, the rotary body is driven to rotate by a prescribed drive force. The contact protrusion on the rotary body contacts and pivots the sensing arm, and a photosensor detects the pivoting motion of the sensing arm. Information about the developing cartridge is determined based on the results of this detection (see Japanese Patent Application Publication no. 2009-244564, for example).